Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Details)

v3.19.2
Stockholders' Equity - Additional Information (Details) - USD ($)
 1 Months Ended 3 Months Ended 6 Months Ended
Jun. 28, 2019
Apr. 30, 2019
Jul. 13, 2018
Apr. 30, 2019
Nov. 30, 2017
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Mar. 29, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Class of Warrant or Right, Exercise Price of Warrants or Rights                   $ 3.47  
Common Stock, Shares, Issued           68,138,203   68,138,203     68,138,203
Common Stock, Par or Stated Value Per Share           $ 0.001   $ 0.001     $ 0.001
Adjustments To Additional Paid In Capital At Market Offering Costs             $ (135,000)   $ (141,000)    
Market Offering [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Proceeds from issuance of Common stock               $ 22,500,000      
Proceeds From Issuance Of Common Stock Net of Issuance Costs           $ 22,000,000   $ 22,000,000      
Common Stock, Shares, Issued           3,500,000   3,500,000      
Common Stock, Par or Stated Value Per Share           $ 6.42   $ 6.42      
Adjustments To Additional Paid In Capital At Market Offering Costs           $ 500,000   $ 500,000      
Aggregate Offering Price of Debt $ 50,000,000                    
Percentage of Placement of Agent Fee 3.00%                    
Available-for-sale Securities           $ 6,800,000   $ 6,800,000      
Common Stock [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Common Stock issued in connection with the first ESPP offering           54,221 43,707 54,221 43,707    
Issuance of Common Stock for At the Market Offering in shares           4,463,399 1,066,038 7,390,826 1,130,835    
Common Stock [Member] | Market Offering [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Average Price Per Share           $ 1.72   $ 1.88      
Proceeds from issuance of Common stock           $ 7,700,000   $ 14,000,000      
Issuance of Common Stock for At the Market Offering in shares           4,500,000   7,400,000      
Adjustments To Additional Paid In Capital At Market Offering Costs               $ 300,000      
Mustang Bio, Inc [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Common Stock Shares Available For Future Issuance Value           $ 20,900,000   $ 20,900,000      
Marketable Securities     $ 75,000,000                
Percentage of Placement of Agent Fee     3.00%                
Mustang Bio, Inc [Member] | Over-Allotment Option [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Proceeds from issuance of Common stock   $ 31,600,000                  
Payments of Stock Issuance Costs       $ 2,100,000              
Proceeds From Issuance Of Common Stock Net of Issuance Costs       $ 29,500,000              
Stock Issued During Period, Shares, New Issues   6,875,000                  
Class of Warrant or Right, Number of Securities Called by Warrants or Rights   1,031,250   1,031,250              
Class of Warrant or Right, Exercise Price of Warrants or Rights   $ 4.00   $ 4.00              
Checkpoint Therapeutics, Inc [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Shares Issued, Price Per Share           $ 4.12   $ 4.12      
Proceeds from issuance of Common stock           $ 4,000,000   $ 4,500,000      
Stock Issued During Period, Shares, New Issues           997,957   1,088,226      
Percentage of Placement of Agent Fee         3.00%            
Maximum Authorized Amount Of Shares To Be Sold         $ 100,000,000            
Available-for-sale Securities           $ 61,500,000   $ 61,500,000      
Checkpoint Therapeutics, Inc [Member] | Market Offering [Member] | Founder Agreement [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Stock Issued During Period, Shares, New Issues           24,941   27,195      
Research and Development Expense [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Allocated Share-based Compensation Expense           $ 800,000 $ 800,000 $ 1,400,000 $ 3,100,000    
General and Administrative Expense [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Allocated Share-based Compensation Expense           2,600,000 2,400,000 $ 5,300,000 4,800,000    
Restricted Stock [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition               5 years 2 months 12 days      
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options           13,600,000   $ 13,600,000      
Restricted Stock Units (RSUs) [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition               2 years 2 months 12 days      
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options           $ 2,100,000   $ 2,100,000      
Employee Stock Option [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Employee Stock Purchase Plan to eligible employees, Reckoning fair value percentage during offering period           85.00%   85.00%      
Common Stock issued in connection with the first ESPP offering               410,728      
Allocated Share-based Compensation Expense           $ 19,000 $ 43,000 $ 39,000 $ 81,000    
Common Stock, Capital Shares Reserved for Future Issuance           589,272   589,272